ApproximateEquality

ApproximateEquality protocol

For numeric types this uses isApproximatelyEqual from Swift Numerics.

DeriveApproximateEquality macro.

Annotate your types with DeriveApproximateEquality to automatically conform to ApproximateEquality and derive an implementation.

DeriveApproximateEquality Example

import ApproximateEquality
import ApproximateEqualityMacros
import CoreGraphics

@DeriveApproximateEquality
public struct MyType {
    var x: Double
    var y: CGPoint
    @ApproximateEqualityIgnored
    var z: Double
    var w: Float
}

let thing1 = MyType(x: 10, y: CGPoint(x: 20, y: 0), z: 30, w: 0)
let thing2 = MyType(x: 10, y: CGPoint(x: 20, y: 0), z: 40, w: 0)
let error = 0.000_001
let thing3 = MyType(x: 10 + error, y: CGPoint(x: 20, y: 0), z: 40, w: 0)

print(thing1.isApproximatelyEqual(to: thing2, absoluteTolerance: 0.0001))      // true
print(thing1.isApproximatelyEqual(to: thing3, absoluteTolerance: 0.0001))      // true
print(thing1.isApproximatelyEqual(to: thing3, absoluteTolerance: 0.000_000_1)) // false

Expanding the @DeriveApproximateEquality macro generates an extension:

extension MyType: ApproximateEquality {
    public func isApproximatelyEqual(to other: Self, absoluteTolerance: Double.Magnitude) -> Bool {
        x.isApproximatelyEqual(to: other.x, absoluteTolerance: Double.Magnitude(absoluteTolerance))
        && y.isApproximatelyEqual(to: other.y, absoluteTolerance: CGPoint.Magnitude(absoluteTolerance))
        && w.isApproximatelyEqual(to: other.w, absoluteTolerance: Float.Magnitude(absoluteTolerance))
    }
}

Note that the property prefixed with @ApproximateEqualityIgnored is used in the implementation.

License

MIT.

Portions of thise code are from the Apple-Numerics (https://github.com/apple/swift-numerics) project and are licensed under the Apache License

TODO

• [ ]: Test against more complex types.
• [X]: Pass through absolute tolerance, norm etc.
• [X]: Handle the casting to Double in DeriveApproximateEquality